Method of producing printing plates



Oct. 21, 1969 R. R. MYERS 3,473,470

METHOD OF PRODUCING PRINTING PLATES Original Filed Oct. 31, 1958 Jnveul'ov Qoberl' 11% era Witnegz g W pwrw US. Cl. Nil-401.1 1 Claim This invention relates to the art of manufacturing printing plates and more particularly to laminated printing plates, with a metal sheet completely imbedded in and surrounded by a plastic.

This application is a continuation of my copending application, Serial No. 770,986, filed October 31, 1958.

The present method of making printing plates is slow and tedious. The prepared printing shells are inverted and subjected to molten backing material. This build up of the shell is relatively thick and after it has cooled and solidified, it then must be trimmed and planed to the correct thickness. Obviously, equipment for performing this necessary process is expensive, usually eliminating this plate preparation from the smaller shop due to the capital investment necessary. Furthermore, there are many difficulties attendant to the manufacture of the conventional printing plate. One objection is the relatively heavy weight of the finished printing plate. One reason for this is that to obtain strength in the plate it is necessary that the backing material be of maximum thickness. The backing material is, of course, exceptionally heavy due to its volume. Most backing material is approximately ninety-four percent (94%) lead, three percent (3%) tin, and three percent (3%) antimony. While the backing material is thus of a very heavy nature, it is not strong and obviously has the possible characteristic of bending. Still another problem is that the finished plates have their edges beveled and are often held to the press by inversely beveled clamp members. Obviously, due to the softness of the backing material, these clamp members may penetrate the plate resulting in the plate becoming loose on the press and buckling and breaking. This combination of objections in the common printing plate places many restrictive limits on the speed on which the press may be operated. In the case of rotary presses, the weight of the plates causes centrifugal force to build up rapidly with the result that the plates tend to bend outwardly and either break or produce undesirable, irregular printing. Still another objection to the common printing plate is the time aspect. Considerable time must be taken in permitting the backing material to cool after it has been placed on the shell. While many plates are manufactured as above indicated, it is also possible to laminate printing plates (electrotypes) with plastic and sheet metal backs.

The procedure herebefore has been to take a printing shell, apply adhesive to its back, place a sheet of plastic onto the adhesive, coat the back of the plastic sheet with an adhesive, and lastly place a sheet of metal onto the last applied adhesive. While this method did produce a lightweight printing plate, it was objectionable in that, first, the metal plate might become accidentally detached from the plastic during either use or processing and, secondly, the metal back plate did not lend itself for shaving, grinding or planing the finished printing plate into one of uniform proper thickness.

Therefore, one of the principal objects of my invention is to provide a lightweight printing plate using both plastic and sheet metal detached from the printing plate either during usage or processing.

A further object of this invention is to provide a laminated printing plate employing with plastic a metal sheet nite States Patent "ice that may be easily processed for desired thickness by grinding, shaving, planing or the like.

More specifically, the object of this invention is to provide a lightweight laminated printing plate incorporating a perforated tough metallic plate wherein the metal plate is imbedded in a plastic backing material.

A still further object of my invention is to provide a lightweight strong printing plate that may be produced rapidly, thereby saving in both labor, time and materials.

A still further object of my invention is to provide a method of making printing plates that requires a minimum of equipment.

These and other objects will be apparent to those skilled in the art.

My invention consists in the method of process, whereby the objects contemplated are attained as hereinafter more fully set forth, pointed out in my claims, and illustrated in the accompanying drawings, in which:

FIGURE 1 is an exploded view of a printing shell, a metallic plate, and a plastic sheet prior to assembly and processing;

FIGURE 2 is an enlarged perspective view of a portion of the perforated metal sheet;

FIGURE 3 is an enlarged cross-sectional view of my plate prior to processing;

FIGURE 4 is a side view of a heated press with the printing shell, metallic plate, and plastic assembly therein prior to the heating and compression operation;

FIGURE 5 is an enlarged cross-sectional view of the finished printing plate unit; and

FIGURE 6 is a side view of a heated press with the assembled parts of the printing plate therein, illustrating the heating of the plastic but prior to the compression operation.

The numeral 10 designates an ordinary printing shell having printing indicia thereon. I recommend before assembling the laminated plate that the back of this printing shell be coated with a suitable glue or adhesive 11. However, if a plastic is used that has highly sticky characteristics when heated, this step of placing an adhesive on the back of the printing shell may be dispensed with. A suitable adhesive would be Bostik 7008.

The plastic sheet that I use has been designated by the numeral 16 and may be of thermoplastic or thermosetting plastic. The plastic may be of any one of several that have been developed such as vinyl acetate-vinyl chloride material. The named material has excellent dimensional stability characteristics and will not shrink after it is compressed.

I have used the numeral 18 to designate the perforated metal plate having holes or perforations 22. This metal plate should be rather rigid and should be tough and strong. While I prefer that the plate be of aluminum, magnesium, or like, it may be obviously of steel, alloys of copper, zinc, or like. If the plate is made of alloys of aluminum, and the finished printing plate is to have an overall thickness of one-fourth (-Mi) inch, this sheet metal should be approximately one hundred twenty-five thousandths of an inch in thickness. This thickness requirement means that the aluminum alloy retains a weight advantage over the sheet steel. The steel, of course, is stronger so that with a balanced press drum, the steel could be nearly as advantageous as aluminum alloy.

In general, my method consists of first placing the perforated metal sheet 18 adjacent the back of the printing shell 10, and the introduction of molten plastic at the back of the perforated metal plate, whereby some of the fiowable plastic will pass through the perforations of the metal sheet and contact and engage the irregular back surface of the printing shell, resulting in the successful imbedding of the perforated metal sheet within the plastic body, as shown in FIGURE 5. The plastics that I have in mind are molten by the application of heat. However, it is conceivable that a cold liquid plastic might be used and which would be capable of hardening either by the atmosphere or by chemical treatment. In either case the finished plate will have plastic at both sides of the perforated metal sheet, and this plastic will also be extending through the perforations of the metal sheet, and the metal sheet will be completely imbedded in and form an integral part of the finished printing plate.

Many advantages are obtained by this process. With plastic at both sides of the metal sheet and extending through the perforations of the same, the metallic sheet will be bonded within the plastic material in all directions. Furthermore, by placing the tough rigid sheet member closely adjacent the printing shell, the relatively fragile printing shell will be successfully supported, and this will result in a more stable printing plate, and better printing efficiency. Still another advantage to this process is that by the metal sheet being perforated, possible air pockets at the rear of the printing shell have an easy escape from the printing plate during the heating and compressing of the printing plate. Obviously, the plastic by passing to the underside ofthe perforated plate will fill up all of the irregularities of the back of the printing shell. By imbedding the perforated metal sheet within the plastic, it is unnecessary to use an adhesive on the metal perforated plate to cause it to stick to the plastic. Also, with part of the plastic at the rear of the metal plate, the plate if necessary may be easily shaped by planing or grinding the back of the same, inasmuch as plastic is easier to grind, shape or plane, than metal.

This is in contrast to the herebefore method of reducing printing plates to suitable thickness by planing, shaving or grinding the metal which herebefore was at the rear side of the printing plate. In the case of laminated plates with metal backs, there was always the hazard in accidentally dislodging the metal plate from the inner core plastic sheet, due to the resistance and toughness of the metal experienced during the planing or shaping operation. With my printing plate, however, this is impossible because, first, the plastic is relatively easy to plane and shape, and secondly, the metal plate is completely imbedded in the plastic and cannod be dislodged during any process of finishing the plate after it has hardened. I further find that by my method even a lighter and stronger, and a more accurate printing plate is produced than has been herebefore possible.

Still another advantage is the rapidity with which my method produces a finished printing plate. I have referred to my finished printing plate as a laminated printing plate, but to all intents and purposes it is, when finished, a solid integral unit and therefore is capable of running off more printed copies than any printing plate yet produced.

My process of producing printing plates may be employed in the fabrication of either flat or arcuate printing plates. Any suitable heated press may be used. As herebefore indicated, the perforated metal plate is laid on the back of the printing shell and on the back of the printing shell is laid a sheet of plastic. These three loose parts are placed in the heated press.

In the drawings I have shown the various laminations of considerable thickness, but this is only illustrative and enlarged for purposes of identification.

The adhesive used on the printing shell may be any suitable glue such as: a thermosetting adhesive of the type which adheres readily and comprising essentially a phenolic resin and a polyvinyl acetate resin in the approximate ratio of 3:1 known commercially as Bostik 7008 and manufactured by the B. B. Chemical Company, of Cambridge, Mass.

The assembled laminations are then placed in a press 25 having the usual compressing jaws 26 and 27. These press cs 25 are heated by any suitable means such as by electric resistance wires 28. These press dies are heated to approximately 300 Fahrenheit. The assembled laminations are then placed between the jaws of the press which are closed without pressure and in approximately three (3) minutes the plastic will become soft from such heating. The press is then closed with approximately one hundred tons pressure until the plastic and adhesive are cured. I have already discussed the pressing of the plastic through the holes of the metal sheet. The press has limiting stops 29. so that the completed plate will be of proper predetermined thickness. The plate is then removed from the press and trimmed.

Also, my method lends itself to plate treatment or premade ready. Merely by placing a sheet of suitable material over the face area to be treated of the printing surface, i.e., between the printing face and the press, the desired results are obtained quickly and cheaply.

Some changes maybe made in my method of and means for producing printing plates without departing from the real spirit and purpose of my invention, and it is my intention to cover by my claims, any modified forms of structure or use of mechanical equivalents which may be reasonably included within their scope.

I claim:

1. The method of making rigid printing plates, comprising, the taking of a printing shell having both sides irregular, the treatment of the back of the printing shell with a heat-activated adhesive, the placing of a perforated rigid metal sheet on the back of said printing shell, the placing of a thermoplastic material-onto the back of said perforated metal sheet, the placement of the assembled plate in a heated press, the application of heat to said assembled press to make said thermoplastic material fiowable and to activate said adhesive, the application of pressure to said assembled plate to cause a portion of the material of said thermoplastic sheet to run through the perforations of said metal sheet to the other side of said metal sheet to separate the metal sheet from engagement with said printing shell; and to contact and fill up the irregularities on the back side of said printing shell, and to imbed the metal sheet within the thermoplastic material.

References Cited UNITED STATES PATENTS 851,049 4/1907 Wood 101-4011 X 1,803,548 5/1931 Drake 10l-395 2,814,990 12/1957 Myers 101-395 X 2,272,254 2/1942 Swan 10140l.l X 2,244,187 6/1941 Cochran 10l-40l.l X 2,632,722 3/1953 Libberton 10l401.2 X

DAVID KLEIN, Primary Examiner US. Cl. X.R. 

1. THE METHOD OF MAKING RIGID PRINTING PLATES, COMPRISING, THE TAKING OF PRINTING SHELL HAVING BOTH SIDES IRREGULAR, THE TREATMENT OF THE BACK OF THE PRINTING SHELL WITH A HEAT-ACTIVATED ADHESIVE, THE PLACING OF A PERFORATED RIGID METAL SHEET ON THE BACK OF SAID PRINTING SHELL, THE PLACING OF A THERMOPLASTIC MATERIAL ONTO THE BACK OF SAID PERFORATED METAL SHEET, THE PLACEMENT OF THE ASSEMBLED PLATE IN A HEATED PRESS, THE APPLICATION OF HEAT TO SAID ASSEMBLED PRESS TO MAKE SAID THERMOPLASTIC MATERIAL FLOWABLE AND TO ACTIVATE SAID ADHESIVE, THE APPLICATION OF PRESSURE TO SAID ASSEMBLED PLATE TO CAUSE A PORTION OF THE MATERIAL OF SAID THERMOPLASTIC SHEET TO RUN THROUGH THE PERFORATIONS OF SAID METAL SHEET FROM ENGAGEMENT WITH SHEET TO SEPARATE THE METAL SHEET FROM ENGAGEMENT WITH SAID PRINTING SHELL: AND TO CONTACT AND FILL UP THE IRREGULARITIES ON THE BACK SIDE OF SAID PRINTING SHELL, AND TO IMBED THE METAL SHEET WITHIN THE THERMOPLASTIC MATERIAL. 